1. Field of the Invention:
This invention relates generally to bicycle hubs, and more particularly to a bicycle hub which is capable of selectively receiving a forward driving force or a backward driving force.
2. Description of the Prior Art:
As is well known, most bicycles are designed to be driven only forward while being also allowed to run idly forward without forward pedalling. For this purpose, one of the hubs (usually rear hub) for such a bicycle is provided with a freewheel which receives a pedalling force but co-rotates with the hub only in the forward rotational direction.
More specifically, a typical freewheel comprises an inner ring fixed to one end of a hub body, and an outer sprocket ring surrounding the inner ring. The sprocket ring is internally formed with a circumferential series of ratchet teeth, whereas the inner ring externally carries a diametrically opposite pair of ratchet pawls which is spring-biased for driving engagement with the ratchet teeth only in the forward rotational direction but passes by the ratchet teeth in the opposite or backward rotational direction. Thus, the forward pedalling force exerted by the cyclist is transmitted to the hub via the freewheel, whereas the backward pedalling of the cyclist results in idle backward rotation of the sprocket ring of the freewheel. Further, the hub can freely rotate in the forward rotational direction to enable idle or inertial forward running of the bicycle without forward pedalling.
The conventional bicycle, which is capable of running only forward, is satisfactory for most purposes. However, such a bicycle is not suitable for particular purposes such as bicycle moto-cross.
Bicycle moto-cross, which has becoming increasingly popular, is a sport event in which the participants compete in their skill of riding in bad road conditions. In one program called "free-style", particularly, each competitor tries to do an excellent and impressive performance by making acrobatic movements which naturally include both forward and backward movements.
With the conventional bicycle, however, the rider can make only forward driving. Therefore, the only way for the rider to make a backward movement is to first go up a slope by forward running to subsequently go down, without a directional change of the bicycle, by utilizing a gravitational acceleration. Obviously, the backward movement obtained in this way causes the bicycle pedals to rotate in the backward rotational direction, consequently giving a danger to the rider.
It is possible to achieve backward driving by the hub with a freewheel which includes an outer sprocket ring co-rotatable, via a reverse ratchet mechanism, with an associated inner ring (i.e., the hub fixed thereto) only in the backward rotational direction. Such a freewheel also enables idle or inertial backward running without forced backward pedal rotation.
The above solution, however, results in inability of driving forward which basically is more imporant than driving backward. Obviously, an excellent performance in a free-style program of the bicycle moto-cross is possible only by dynamic combination of forward and backward movements. Therefore, the reverse working freewheel is disadvantageous for the purpose of bicycle moto-cross as well as for normal use.